1. Field of the Invention
The present invention relates to an automatically controlled irrigation system. The system includes pressurized porous capsules that are installed in the soil to determine the level of moisture for irrigation. The depth of the capsules in the soil will depend, among other factors, on the crop to be irrigated and on the development of the roots. The capsule functions through the depressurization of the interior of the capsule due to loss of pressurized gas to the soil in response to the opening of the capsule pores when the soil moisture rises to a value corresponding to a capsule outside pressure which is lower than the capsule inside pressure. This gas depressurization acts on appropriate devices, such as differential valves and pressure switches.
The irrigation may be activated by appropriate devices, such as, for example, pressure switches, differential valves, level controlling ball-floats, etc.
2. Background of the Invention
The available soil irrigation systems present various levels of complexity and may be divided in two groups. The criterion for such division is whether or not they depend on the soil moisture as the determining parameter for the moment to activate irrigation. The independent systems are automatically activated at previously set time intervals based on soil and weather conditions, and on the type of plant, ignoring, thus, the plants"" real needs. Examples of such systems are described in U.S. Pat. No. 5,882,141 and EP 71176.
Thus, the quantitative determination of the best moment to irrigate remains a challenge. Such decision is usually based on empirical and qualitative criteria, and the commercial use of soil moisture sensors for irrigation control is still, generally speaking, very limited. Some of the best known sensors are the porous capsule tensiometers, which operate in a regime of moisture saturation.
Irrigation systems that use porous capsules or other similar sensor elements fixed to the ground do not always do so as a means of measuring the soil moisture. The systems described in U.S. Pat. No. 3,840,182 and FR 2196744 may be cited as examples of such a porous element which has the function of controlling the release of water so that a plant may have practically continuous supply of water, independent of the soil""s saturation level. A disadvantage of such systems is that if the natural evaporation rate is higher than expected, the water supply might not be sufficient to provide for the plants"" needs.
Tensiometers have also been used to measure the soil moisture. However, the tensiometers used for irrigation control are usually quite large, so as to be able to activate the mechanical or electronic pressure switches without the need for an excessively long response time. Even portable tensiometers for soil moisture measurement as described in U.S. Pat. No. 4,068,525 have this problem. This problem is aggravated by accumulation of air within the tensiometer""s pipes. Due to their compressibility, the air bubbles cause the volumes of water exchange per tension variation unit to increase exponentially as the water tension module asymptotically approaches the barometric pressure. Therefore, the tensiometers are limited to a range of work between zero and the barometric pressure. The limitation occurs even in the tensiometers whose capsules are covered with thinly porous material, in which such limitation persists due to the air bubbles that form in the larger cavities connecting the capsule to the pressure sensor. Besides, the thinly porous capsules have low hydraulic conductivity, a fact that makes the response time too long. U.S. Pat. No. 4,567,563 describes an irrigation system with a tensiometer which has been made more automated and complex in order to provide for the limitations of such type of moisture gauge.
The limitations presented by tensiometers may also be solved by the system described in U.S. Pat. No. 3,874,590, which determines the soil moisture through a sensor based on the expansion and retraction properties of a water absorbent material in contact with the soil. The sensor commands an on/off valve that starts irrigation when the absorbent material is retracted (dry soil) and cuts the water supply when the material is fully expanded (moist soil). This kind of sensor presents the same disadvantages as the tensiometers.
Document BR PI 9003611 presents the hydro-marker (hidrobalizador), a sensor used in irrigation systems which determines the soil moisture""s point of recharge based on the energy balance of the water in the soil, considering the critical point of the water layer available to the soil, avoiding complex calculations and interpretations that require qualified personnel. Such a device is presented as a means to eliminate the disadvantages of the tensiometers known in the market. It does not, however, solve one of the negative characteristics of previous tensiometers, i.e., the fact that they operate under moisture saturation.
A system that overcomes the difficulties presented by automatic irrigation systems based on sensors such as tensiometers is desired.
The invention relates to an irrigation control system comprising; at least one porous capsule sensor, a pressurized gas source in fluid communication with the at least one capsule sensor, and a pressure sensor configured to detect a change in gas pressure in the capsule sensor, wherein the pressure sensor is configured to control irrigation. The invention also relates to a method for monitoring soil moisture conditions comprising, providing at least one porous capsule sensor, placing the at least one porous capsule sensor in the ground, pressurizing the at least one porous capsule sensor with gas, and monitoring a gas pressure associated with the at least one porous capsule sensor. The irrigation water is controlled based on the gas pressure in the capsule sensor.
One aspect of the present invention is to provide an automatic irrigation system that uses pressurized porous capsules to determine whether soil contains enough moisture, or whether the soil requires further irrigation. In this system, the water within the porous capsule is replaced by a gas under lower pressure than that necessary to force air through the pores of a capsule submerged in water. The pressure below which air will not pass through the wet pores of the material comprising the porous capsule is referred to in this document as the bubbling pressure.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention, and, together with the description, serve to explain the principles of the invention.